The present invention relates to an apparatus for dry-distributing of fibrous materials for the formation of a course of fibrous material, and more specifically an apparatus of the type which is disclosed in EP-C-0032 772 (DK Patent No. 149979). The apparatus has a forming head which is disposed immediately above a moving wire mesh, under which there is a suction box for the creation of a downwards-leading flow of air in the forming head. This head is configured as a bottom-less and top-less box which extends transversely to the wire mesh and contains a pair of parallel, rotatable drums consisting of perforated plates. At their respective opposing ends, these drums are flow-connected by means of channel bends at 180°, and through the one or the both of these there is blown a stream of air-fluidised fibre which thus circulates axially through the drums.
A part of the air from the suction box that is sucked down through the forming box will pass transversely through the perforated drums, and herewith have a leading-out effect on the fibres, which is supported by the rotation of the drums, which in themselves have a slinging-out effect on the air and herewith on the fibres in the drums. It has been ascertained that with this technique an advantageous distribution of the fibres can be achieved over both the length as well as the breadth of the wire mesh, as well as a quite high capacity for the plant.
In the handling of air-fluidised fibre, problems can easily arise with regard to static electricity, which can not only promote the formation of clumps in the fibres, but can also lead to the attraction of fibre clumps towards the swept surfaces such as the inner sides of said forming box. Therefore, with the relevant technique it is advantageous that a second part of the sucked-down air is brought to flow down into the clearance arising between the pair of drums and the inner sides of the forming box, in that this air can thus remove fibres and small clumps of fibres which adhere to these side surfaces.
However, with the present invention it has been realised that these conditions can be changed considerably by a modification which in principle is quite simple, namely that by means of upper cover plates, a covering can be established of the slot spaces between upper, upwardly-exposed parts of the drum cylinders, and respectively between the drum cylinders, and the spaces between these parts and the adjacent inner sides of the forming box. This would immediately appear to be controversial, the reason being that precisely the sluicing effect which the sucked-down air exercises on the inner sides of the forming box would, after all, be annulled, but the modification must be seen primarily in the light that it will force all the air which is sucked down to pass down through the drums, which will radically change the operational conditions.
Firstly, the dosing-out capacity of the drums will be increased to a particularly distinct degree, typically by no less than 60-70%. Secondly, the emission of air/fibre from the lower parts of the drums will be so intensified that this emission in itself can counteract the mentioned accumulation of fibres on the inner side of the forming box. The same will apply to a possible accumulation of fibres on the outer side of the drum cylinders around their perforations, as the fibres will be blown out through these openings with greater force than has hitherto been the case, and thus it is a realistic possibility to be able to completely avoid the arranging of hitherto-necessary means such as rotating brush rollers for the cleaning of the outer sides of the drum cylinders.
Moreover, it has proved that the improved result can be achieved while using a reduced suction effect, i.e. with a reduced consumption of energy.